Most paving machines now-a-days for laying bituminous or asphalt roadways are of the so-called "floating screed" kind. Each employs a tracked or wheeled tractor unit having a pair of rearwardly extending screed pull arms pivoted to its sides, the screed assembly itself being attached to the rear ends of the pull arms. In this type of paver the texture and density of the mat is influenced by the weight of the screed assembly, since it "floats" upon the material beneath it, and by the angular attitude of the underlying screeding surface relative to the roadway, known as the "attack angle" of the screed. For a given paving speed the thicker the mat being laid the greater the attack angle must be in order to achieve a required mat density. Hence the screed assembly in turn must be pivoted relative to the pull arms about a transverse axis so that the attack angle can be adjusted on the run as conditions dictate.
A typical width of the screed assembly of a paver for highway and the like construction is ten feet, approximately the overall width of the paver itself. In order to lay a mat of greater width, and so reduce the number of passes needed, extensible screed assemblies are commonly used. These include a pair of shorter screeds, or "screed extensions" as they are often called, carried by and disposed rearwardly of the main screed, being attached to the latter so that one or both can be slid longitudinally outwards of the main screed and so extend the effective width of the latter up to twofold. The overall width of the mat laid in a single pass is thereby increased and also the efficiency of the paver in terms of time and cost needed to pave a given roadway. But inherent in the use of screed extensions are certain deficiencies which have not been recognized or if recognized have simply been ignored in practice.
These deficiencies arise from the fact that as the width of the screed assembly is increased by the extensions the weight upon the portion or portions of the mat being laid by the extensions as well as the main screed decreases, especially towards the outer ends of the extensions. The result is a mat of uneven or variable texture and density. Another problem results when one screed extension strikes a curb, a manhole cover or the like, a not infrequent or isolated occurrence during some paving conditions. The screed extension is thereby often thrown out of alignment with the main screed, thus altering the effect of the attack angle of the extension on the mat and so the texture of the latter. Accordingly, the chief object of the present invention is an improved extensible screed assembly which eliminates or at least reduces the deficiencies mentioned as well as incorporating other improvements in structure and ease of operation.